An attempt was made to elucidate relationship between magnitude of nocturnal blood pressure decline (NBPD) and the state of left ventricle in patients with essential hypertension. Data obtained in 166 male patients of various age showed that patients with pronounced and insufficient NBPD had significantly different left ventricular myocardial mass and end-diastolic volume. On the other hand relationship between changes of the heart and NBPD depended on age: in patients younger than 25 years greater dimensions and mass of the heart were associated with pronounced NBPD while in older patients - with insufficient NBPD. it is concluded that inadequate NBPD can facilitate secondary changes of the heart while development of hypertrophy and dilation of the left ventricle can cause diminishment of the nocturnal fall of blood pressure.